Electronically timed relay



Feb. 13, 1951 s. A. TUCKER Erm.

ELECTRONICALLY TIMED RELAY Filed Feb. 20. 1947 mw wm .NQ Ew w ma M M ww .3ST .$51

Passed r-jeb. 13, 1951 ELECTRONICALLY TIMED RELAY Spencer A. Tucker, New York, and Alvin W. Gellert, Rego Park, N. Y.

Application February 20, 1947, Serial No. 729,776

8 Claims.

Our present invention relates to an electronic timer and aims to provide certain improvements therein. More specically, it relates to a timer designed particularly for photographic contact printers, enlargers. blue printing machines, photostat making machines, etc., although it is equally well adapted for use in other industrial and scientific fields wherein any type of electrical apparatus or device is to be operated for a predetermined interval of time.

Electronic timing devices are known and have been used for many years in the photographic and industrial fields. In all of these prior devices of which we have knowledge, the accuracy of the selected time interval, the time range, or the means for setting the time interval are not entirely satisfactory because they are unreliable, too costly, or require a bright light for increased visibility or extreme care for setting means which govern the timing interval.

The foregoing objectionable features of prior devices are overcome by our present invention according to which upon the closing of an initiating switch in a vacuum tube circuit, electric current is caused to flow through a load circuit, and after a predetermined time interval which is governed by the rate of discharge of capacitance through resistance in the vacuum tube circuit, the iiow of current through the load circuit is automatically cut off. After completion of the desired operation by the device within the load circuit, the timer is ready for the next operation, which can be initiated by again merely operating the initiating switch. The invention which includes a modified Eccles-Jordan trigger or "flipiiop" circuit having therein a relay, an initiating switch and an adjustable resistive-capacitive network will be better understood from the detailed description which follows when considered in connection with the accompanying drawings wherein:

Fig. l shows a preferred circuit diagram for the electronic timing device embodying our invention; and

Fig. 2 is a diagrammatic showing of our novel time selector switch assembly illustrating one arbitrary setting of the switch members thereof.

Referring to Fig. 1 of the drawings, electric current, either A. C. or D. C., islsupplied to the device by inserting a connector plug II'I into a suitable outlet receptacle (not shown). One of the leads from the plug is connected through a manually operable switch I I to a ground or common connection in said circuit. The other lead from the plug which completes the circuit is connected to the heater elements and to the plates of the diode sections of a pair of vacuum tubes I2 and I3, or any equivalent rectifier, in a conventional manner to provide half wave rectification where A. C. is employed. As herein shown, the cathodes of the said diode sections of the vacuum tubes are connected together and also connect with the plates and the screen grids I6- and I5 of the pentode sections of said vacuum tubes I2 and I3 respectively or the corresponding elements of other electron tubes. Within the branch circuit connecting with the plate of the pentode section of tube I2 is a relay I6 and a voltage dropping resistor I1 which properly matches the output characteristics of tube I2. Within the branch circuit connecting with the cathodes of the diode sections of tubes I2 and I3 is a filtering condenser I8. Within the branch circuit connecting with the screen grid I5 are resistors I9 and 20. The cathodes of the pentode sections of tubes I2 and I3 are connected together and in said connecting line there is connected a potentiometer 2l which serves as a calibration control which determines the critical point at which the circuit will iiip or trigger. The contact arm of the potentiometer is connected to ground through a resistor 22. Connected to the line leading to the plate of the pentode section of tube I2 is a branch circuit containing a manually controlled, self-opening, initiating switch 23 controlled by a spring 23a, a condenser 24, a second condenser 25 and a resistor 26. Coupled in the circuit between the two tubes I2 and I3 is an adjustable capacitive-resistive arrangement or network herein shown as consisting of a, timing condenser 21, and a. time selector switch assembly indicated generally by the numeral 28, which latter is interposed between the control grid 29 of tube I3 and the cathode of tube I3. A power receptacle outlet 30 is adapted to be connected to the power source when the relay I6 is energized by the closing of the switch 23. The outlet 30 is also adapted for direct connection with the power source independently of the timing circuit, through the connector plug I0 and for this purpose a manually controlled switch 3| is inserted in this separate circuit. In photographic use, the switch 3l would be used for focusing the enlarger prior to initiating the timing cycle. A neon pilot lamp 3Ia with a proper voltage dropping resistor 3Ib may be provided for furnishing sufficient illumination for setting the push buttons of the selector switch 28 and for other purposes.

The relay I6 is preferably of the `vdouble pole, double throw type, having its poles 32 and 33 shown as spaced from the armature |611. of relay I6 for clarity of illustration and said poles are annuo adapted when the relay is energized to make contact with contacts 34 and 35 respectively. which in turn connect with the control grid 2s of tube I3 and a lead to the power outlet 3d respectively.

The time selector switch assembly 23 as shown in Fig. 2 contains seven push button switches 35 to 42 inclusive. controlling resistors 43 to 43 respectively and provides a resistive-capacitive network with the condenser 2l which has a special low leakage characteristic. The switches 36 to 42 are prexerably of the push button type. each being a single pole, single throw. normally closed switch. Each of the switches is shunted across a resistor which it controls. When no button is depressed all seven resistors are shortcirculted. By depressing any one of the seven buttons or switches, the corresponding resistor is admitted into the circuit. Depressing any combination of these switches places the corresponding resistors in series thereby increasing the time constant of the network. The resistors 43 to 49 in the ascending order of their designating numbers are preferably so chosen that the admitting of resistor 43 will have a time constant discharge of one second, resistor 40 a time constant of two seconds. and each succeeding resistor a time constant twice as large as its preceding numbered resistor. In other words the time constants of the resistors 43 to 43 are in geometrical progression. With seven resistors as shown it will thus be seen that by admitting one or more of them any time constant for discharge of condenser 21 from 1 second to 127 seconds. in one second steps, can be obtained. It will also be apparent that by increasing the number of buttons and resistors the time selector range may be increased indefinitely. each additional switch and resistor doubling the range o! the timer achieved with the previous number of switches. As shown in Fig. 2 switches numbered 33, 31, 33'and 40 are open thus providing for the sum of timing constants of 1, 2, 8 and 16 seconds or a 27 second timing interval for discharge of the condenser 21. Although push button switches are referred to, it will be obvious that toggle switches, lever switches or any other switching mechanism may be employed. It will also be apparent that if desired a decade multiplier switch may be coupled with a plurality of timing condensers whereby the time intervals provided by the switches 38 to 42 may be changed in decade steps.

In the circuit shown and described, the cathode of each diode section of the tubes is positive and the high capacitance of condenser I3 acts to smooth any voltage pulsations resulting in a D. C. of lower ripple content. As a result of rectification, a positive D. C. voltage is impressed on the plate and on the screen grid of each pentode section of each tube. The resistor I1 and relay I3 provide a path for the positive voltage to appear on the plate ot tube I2 and the resistor I9 provides continuity of a positive voltage on screen grid I5. The potentiometer 2| is the calibration control which determines the critical point at which the circuit will nip or trigger. Condenser 2l is used to prevent arcing and pitting of the contacts at switch 23. Resistor 2B serves to discharge condenser 25 so that it will be ready to accept a new initiating voltage charge. Resistors I9 and 20 provide the correct voltage for the screen grid I3.

Operation-Upon inserting plug I3 into a socket supplying electric current, either A. C. or D. C. and then closing switch II, rectified and filtered D. C. is supplied to the modiiled Eccles-Jordan vacuum tube circuit containing tubes I2 and I3. In the quiescent state of the timer. tube I3 will be conducting current and tube I2 will be non-conducting. 'I'he desired time interval is chosen by actuating the proper switch or combination of switches in the time selector switch assembly 23. which in turn admits into the circuit the corresponding value of resistance from the resistors 43 to 49. The timing cycle is initiated by momentarily closing the starting switch 23. Instantaneously upon the closing of the starting switch, the relay I3 is caused to close by virtue of a high initial charging current of starting condenser 25 flowing through the relay I3. The instant the relay closes, the poles 32 and 33 thereof engage contacts 34 and 35 respectively. Contact between pole 33 and contact 33 completes the circuit from the power source to receptacle 33 thereby supplying current to the load circuit at the power receptacle 30. Simultaneously. contact between pole 32 and contact 34 causes vacuum tube I3 to cease drawing current as a result of an applied negative voltage on the control grid 28 from the negative side of condenser 21. Since vacuum tube I3 is now not conducting. a Positive voltage which previously existed at the cathode of the pentode section of tube I2 is no longer present, thus causing vacuum tube I2 to conduct and resulting in a ilow of plate current through the relay I6 thereby keeping the relay energized. While vacuum tube I2 is conducting (and the relay is closed) the negative voltage which appears at the control grid 29 of tube I3 is diminishing at a ratedetermined by the value of the resistance selected with the time selector switch 23. When this negative voltage has dropped to such a value which will permit vacuum tube I3 to conduct, a positive voltage will be placed at the cathode of the pentode section of vacuum tube I2 causing the current which was flowing through said vacuum tube and through the relay I3 to cease, thereby releasing the relay armature thus lbreaking contact at points 34 and 35 and breaking the current now to the load circuit. The timing cycle is thus completed and the timer is now ready for another cycle.

The timer can be used with a D. C, source of current, In which case the direct current is pure andunvarying and the diode sections of the vacuum tubes will pass current continuously instead of only half the time when A. C. is used.

While `it will be understood that the circuit specifications of the electronic timer may vary according to the design for any particular application, the following circuit specifications for a timer particularly suitable for photographic printing and the like are included by way of example only, as follows:

Resistors 2li-30K 3| b-150K, 10% i3-0.159 megohms, 2%

44-0.318 megohms, 2% 45-0.636 megohms, 2% lli-1.270 megohms, 2% 41-2.54'megohms, 2% "-5.10 megohms, 2% 43-1020 megohms, 2%

Capacitors l8--20 mid. 150 v.-e1ectrolytic 24-0.1 mfd. 200 v.-paper tubular 25-10. mfd. 150 v.-electrolytic 21-3.0 mid. 5% 200 v. oil lled paper The vacuum tubes I2 and i3 are type 11'! N'IGT.

While we have shown and described what we 1'believe at present is considered the preferred embodiment of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention as defined in the appended claims.

What we claim is:

l. An electronic timer for controlling the energization of a load circuit comprising a flip-flop trigger circuit including first and second electron discharge tubes each provided with a cathode, a control grid and an anode, and circuit means to apply positive potentials with reference to ground to the respective anodes of said tubes, said first tube being normally non-conductive and said i second tube being normally conductive, a relay including an electromagnetic winding and a switch actuated thereby, said winding being interposed in the anode circuit of said rst tube, said switch having first and second contact positions and normally occupying said iirst position, a timing condenser having one end connected to the anode of said first tube and the other end connected selectively through said switch in the rst position to ground and through said switch in the second position to the control grid of the second tube. said condenser attaining a charge when connected to ground, a variable resistance element for discharging said condenser and connected between the control grid and the cathode of said second tube, means to apply momentarily an energizing current through said winding to actuate said switch and connect said condenser to the control grid of the second tube, the charge on said condenser rendering said second tube non-conductive whereby said rst tube is rendered conductive, the conduction through said rst tube maintaining said winding energized for a period determined by the time constant of said condenser and said element, and means responsive to the actuation of said switch for energizing the load circuit.

2. An electronic timer for controlling the energization of a load circuit comprising a iiip-op trigger circuit including rst and second electron discharge tubes each provided with a cathode, a control grid and an anode, and circuit means to apply positive potentials with reference to ground to the respective anodes of said tubes, said first tube being normally non-conductive and said second tube being normally conductive, a relay including an electromagnetic winding, said winding being interposed in the anode circuit of said iirst tube, a main and an auxiliary switch actuated thereby, said main switch having first and second contact positions and normally occupying said rst position, said second switch being normally open, a timing condenser having one end connected to the anode of said first tube and the other end connected selectively by said main switch in first position to ground and in the second position to the control gridof the second tube, said condenser attaining a charge when connected to ground, a variable resistance element for discharging said condenser and connected between the control grid and the cathode of said second tube, means to apply momentarily an energizing current through said winding to actuate said main switch and connect said condenser to the control grid of the second tube, the charge on said condenser rendering said second tube non-conductive whereby said iirst tube is rendered conductive, the conduction through said first tube maintaining said winding energized for a period determined by the time constant of said condenser and said element, and a source of energizing voltage for said load circuit connected thereto through said second switch, said load being connected as long as said winding is energized.

3. An electronic timer for controlling the energization of a load circuit comprising first and second electron discharge tubes each provided with a cathode, a control grid and an anode, a source of direct-current potential for said tubes, the negative end of said source being connected to ground, a voltage-dropping impedance, a relay including an electromagnetic winding and a switch actuated thereby, said switch having first and `second contact positions and normally occupying said rst position, the positive end of said source being connected to the anode of said second tube and in series with said winding and said impedance to the anode of said first tube, a bias resistor connected between ground and the cathodes of said tubes, the potentials normally on the electrodes of said tubes having values at which said second tube is conductive and said iirst tube non-conductive, a timing condenser having one end connected to the anode of said rst tube and the other end connected selectively by said switch in the first position to ground and in the second position to the control grid of said second tube, said condenser attaining a charge when connected to ground, means connecting the control grid of said rst tube to ground, a variable resistance element for discharging said condenser and connected between the control grid and cathode of said second tube, means to apply momentarily an energizing current through said winding to actuate said switch and connect the charged condenser to the control grid of said second tube to render same non-conductive whereby said first tube is rendered conductive, the conduction through said rst tube maintaining said winding energized for a period determined by the time constant of said condenser and said element, and means responsive to the actuation of said switch for energizing the load circuit.

4. An electronic timer, as set forth in claim 3, wherein said means to apply momentarily an energizing current through said Winding includes a capacitor and self-opening switch connected in series with said capacitor between ground and the junction of said impedance and said winding.

5. An electronic timer, as set forth in claim 3, wherein said variable resistance element includes a plurality of serially-connected resistors having mutually different values and a like plurality of switches each connected in shunt relation with a respective resistor.

6. An electronic timer, as set forth in claim 5, wherein the successive values of said serially-connected resistors diirer in accordance with a geometrical progression.

7. An arrangement. as set iorth in claim 3. wherein said impedance has a value substantially matching the output impedance of said rst tube.

8. An electronic timer for controlling the energization oi a load circuit comprising ilrst and second electron discharge tubes eachy provided with a cathode. a control grid and an anode, a

source of direct-current potential for said tubes, the negative end of said source being connected to ground. a voltage-dropping impedance, a relay including an electromagnetic winding and a switch actuated thereby, said switch having first and second contact positions arid normally occupying said first position, the positive end -of said source being connected to the anode of said second tube and in series with said winding and said impedance to the anode of said first tube.

a potentiometer having an adjustable arm and interconnecting the cathodes of said tubes, a bias resistor connected between ground and said adjustable arm, the potentials normally on the ylance element for discharging said condenser and connected between the control grid and cathode of said second tube. means to apply momentarily an energizing current through said winding to actuate said switch and connect the charged condenser to the control grid of said second tube to/ render same non-conductive whereby said first tube is rendered conductive, the conduction through said first tube maintaining said winding energized ior\ a period determined by the time constant of said condenser and said element, and means responsive to the actuation oi.' said switch for energizing the load circuit, said last named means including an auxiliary switch actuated by said winding.

SPENCER A. TUCKER.

ALVIN W. GEILERT.

REFERENCES CITED The following references are of record in the le of this patent: v

UNITED STATES PATENTS Name Date Waring July 19, 1892 Aronson May 7, 1907 Van Valkenburg May 18, 1909 Pritchard Aug. 11, 1942 Eisenberg l. Mar. 12, 1946 OTHER REFERENCES Number 

